This application is claims priority of French application no. 0116365 which was filed on Dec. 18, 2001, and was not published in English.
The invention relates to a process for installation of a landing gear on an aircraft structure. More precisely, the invention relates to an installation process for positioning the landing gear with the required precision, regardless of the manufacturing tolerances of the said structure, and particularly when the tolerances are greater than this precision.
The invention also relates to an installation device with an adjustable ball joint designed to implement this process.
The invention also relates to an aircraft fitted with landing gear which is installed according to this process.
The process and device according to the invention may be used on all aircraft. However, they are particularly suitable for large and very large carrier aircraft in which the landing gear and the structure in which it fits are large.
Landing gear is usually installed on an aircraft structure through several hinge shafts parallel to each other and the ends of which are supported by ball joints inserted in reamings formed in the said structure.
Manufacturing tolerances for the aircraft structure are particularly related to part machining and positioning tolerances, and to temperature variations and deformations of the structure when it is assembled.
In general, these manufacturing tolerances are compatible with the required positioning precision of the landing gear with respect to the said structure.
However, it is possible that manufacturing tolerances are greater than the required precision for positioning the landing gear with respect to the structure. This situation arises particularly when the dimensions of the landing gear and the structure into which it fits are large. For example, this is the case for large and very large carrier aircraft.
This problem can be solved by machining reamings in the structure with a diameter less than the required diameter for the placement of the ball joints, leaving a collar with a thickness greater than manufacturing tolerances around the periphery of each of the reamings. The reamings corresponding to the ends of the different hinge shafts used to assemble the landing gear are then machined subsequently on the assembly line using an appropriate machine.
The machine used for this purpose then comprises a basic element with an appropriate stiffness and machining means fixed on this element. The positions of the machining means are defined so that the different reamings can be machined at their theoretical positions, with tolerances less than the required precision. The machining thus achieved concerns firstly the position of the reamings in the X, Z plane of the structure, and secondly surfacing of the collars in order to obtain the required position of the ball joints along a Y axis perpendicular to the said plane and coincident with the axis of the corresponding hinge shaft.
However, there are several disadvantages with this solution.
Some of these disadvantages are related to the machine. Thus, its cost is high and it is large. Therefore, it requires a large storage area outside production periods during which it is used. It is also a complex machine, which can be expensive and difficult to maintain. Furthermore, the use of such a machine requires additional time during assembly of the landing gear. This time may be about 10 days in the case of a landing gear for a large carrier aircraft, which is very undesirable.
Other disadvantages concern for example the difficulty of making a surface treatment of machined parts on the assembly line, the risk of deformation of the structure after the machine is removed, particularly due to stresses induced in the material during machining, etc.
Furthermore, document JP-B-56052622 describes a device to adjust the position of the intersection point of the Y axis of a hinge shaft in the X, Z plane of the support structure. However, this device does not enable the hinge shaft to be supported by a ball joint. Therefore, it is not suitable for the attachment of a landing gear, particularly in the case in which the two parts of the structure in which the opposite ends of the landing gear hinge shafts fit are not parallel due to manufacturing tolerances of the said structure. Furthermore, an aircraft landing gear is usually installed using ball joints, due to possible deformations of the structure particularly during aircraft taxiing periods.
The purpose of the invention is precisely to eliminate at least some of the disadvantages according to prior art.
More precisely, the invention relates to a process and a device for installation of an aircraft landing gear, in which the innovative design positions the said landing gear with the required precision even when the manufacturing tolerances of the structure on which it is installed are greater than this precision.
According to the invention, this objective is achieved by means of a process for assembly of at least one hinge shaft of the landing gear on an aircraft structure, through two ball joints connected to the said structure, characterized in that it comprises the following steps:
measurement of the differences between the theoretical and the real positions of the centers of the ball joints;
actuation of adjustment means associated with at least one of the said ball joints, to bring the centers of the ball joints into their theoretical position;
blockage of the said adjustment means; and
installation of the hinge shaft in the ball joints.
Use of this process makes it possible to adjust the position of the pivot point of the ball joints along three orthogonal directions. The landing gear can thus be positioned precisely, regardless of the manufacturing tolerances of the structure that supports it.
Preferably, actuation of the adjustment means comprises actuation of axial adjustment means capable of displacing the centers of the ball joints parallel to the axis of the hinge shaft and actuation of radial adjustment means capable of displacing the centers of the ball joints in a plane perpendicular to the axis of the hinge shaft.
Advantageously, actuation of the axial adjustment means then consists of placement of at least one thickness shim between the collars formed on a ring connected to the structure and to a cage of the ball joint.
Also advantageously, actuation of the radial adjustment means comprises a first rotation of an outer cage of the ball joint in a first reaming formed in a ring fixed to the structure, and a second rotation of an inner cage of the ball joint in a second reaming formed in the said outer cage of the ball joint, in an eccentric position offset from the axis of the first reaming, the said inner cage comprising a spherical inner surface offset from the axis of the second reaming and in which the ball of the ball joint fits. The first rotation causes displacement of the second reaming formed in the outer cage of the ball joint around the axis of the first reaming, formed in the ring. The second rotation causes displacement of the spherical inner surface formed in the inner cage of the ball joint around the axis of the second reaming formed in the outer cage of the ball joint.
In this case, a ball joint is preferably used in which the second reaming and the spherical inner surface are eccentric by the same distance e, offset from the axis of the first reaming and from the axis of the second reaming.
According to an advantageous improvement to the invention, the radial adjustment means are actuated without disassembly of the ball joint.
Also advantageously, the step to actuate the adjustment means is preceded by a step to place marking means on the structure or on a ring fixed to the structure and in which the ball joint is installed.
The invention also relates to an aircraft in which the landing gear is installed using such a process.
The invention also relates to a device for installation of a landing gear hinge shaft on an aircraft structure, the said device comprising at least one ball joint comprising a cage that can be fixed on the structure and a ball that can support the said hinge shaft, and being characterized in that the cage comprises an outer cage that can be fixed on the structure, the said outer cage being centered on a first axis and with a reaming with an axis offset from the first axis, an inner cage installed free to rotate in the reaming and with a spherical inner surface with its axis offset from the reaming axis, and means of blocking the inner cage and the outer cage in determined angular positions in which the outer cage is installed in a ring provided with marking means and that can be fixed on the structure.